To expand on this, so if you take a photo and it is too dark, you can brighten it up by opening the aperture (ie go to f2.8 from f4), slowing the shutter speed (ie go to 1/100 from 1/250) or by boosting the ISO (go to 1600 from 800)

If you take a photo and it is too bright, you could close the aperture (go to f4 from f2.8), speed up the shutter (go to 1/250 from 1/100) or lower the ISO.

This is instead of using exposure compensation.

The reason it is called manual mode is because you get to choose which method (ie ISO, shutter or aperture) you use to brighten or darken the image.

The needle says how dark-light the picture will be. In semi-auto modes you can say how dark/light it has to be, in the fully manual mode you have to set the settings to get the needle on the right place.

Exactly the same. This type lightmeter is used for over 30 years, so I guess there´s nothing wrong or strange with it.